Radio frequency identification tag location estimation and tracking system and method
View Patent ↗Systems and methods for locating one or more radio frequency identification (RFID) tags are provided. A phase difference of received information signals of illuminated RFID tags is utilized to locate the RFID tags. One or more exciters transmit interrogation signals to illuminate the RFID tags in which the exciters may have a plurality of antenna selectively configured to transmit through two or more antennas and to receive on one antenna. Multiple reads of the same RFID tag can also be performed to generate a probability model of the location of the RFID tag. An enhanced particle filter is applied to probability model to determine the exact location of the RFID.
1. A method of locating one or more radio frequency identification (RFID) tags comprising:
illuminating at least one RFID tag by an exciter using a plurality of frequencies;
receiving information signals from the illuminated at least one RFID tag by a plurality of receive antennas;
determining a group delay for the received information signals from the at least one illuminated RFID tag received by each of the plurality of receive antennas;
determining the path length between the exciter, the at least one illuminated RFID tag, and each of the plurality of receive antennas using the determined group delay of the received information signals at each of the plurality of receive antennas:
determining a plurality of ellipses based on the locations of each of the plurality of receive antennas, the location of the exciter, and the determined path lengths; and
identifying a location of the at least one RFID tag based on the determined ellipses.
2. The method of claim 1 further comprising transmitting an activation signal from a reader to an exciter, the reader and exciter sharing a common geometric characteristic relative to each other.
3. The method of claim 1 wherein the shared common geometric characteristic is an ellipsoid wherein the reader and the exciter are foci of the ellipsoid.
4. The method of claim 1 wherein identifying the location of the at least one RFID tag is based on a frequency derivate of the received information signals.
5. The method of claim 1 wherein identifying the location of the at least one RFID tag is based on a ratio of the phase derivate versus the frequency derivate.
6. The method of claim 1 wherein identifying the location of the at least one RFID tag is based on a read rate derivate of the received information signals.
7. A radio frequency identification (RFID) system for locating one or more RFID tags, the system comprising:
a plurality of antennas configured to selectively transmit interrogation signals through at least two of the plurality of antennas and to selectively receive information signals from at least one RFID tag through one of the plurality of antennas different from the at least two of the plurality of antennas; and
a reader configured to:
activate the antennas configured to selectively transmit interrogation signals;
determine the path length between the receive antenna, the at least one illuminated RFID tag, and each of the plurality of transmit antennas using the determined group delays of the received information signals;
determine a plurality of ellipses based on the locations of each of the plurality of receive antennas, the location of the transmit antenna, and the determined path lengths; and
identify a location of the at least one RFID tag based on the determined ellipses.
8. The system of claim 7 wherein the plurality of antennas are arranged in a uniform pattern.
9. The system of claim 7 wherein the plurality of antennas are positioned equidistant from each other.
10. The system of claim 7 wherein at least two of the plurality of antennas are positioned as foci for a substantially ellipsoid that identifies a locus of potential locations of the at least one RFID tag.
11. The system of claim 7 wherein the plurality of antennas are positioned in pairs with each pair being foci for a substantially ellipsoid that identifies a locus of potential locations of the at least one RFID tag and each pair positioned to minimize overlapping of each substantially ellipsoid.
12. The system of claim 7 wherein the plurality of antennas are positioned around the at least one exciter, each location of each of the plurality of antennas differing from each other.
13. The system of claim 7 wherein the exciter uses a carrier frequency to mix a reference signal with the received information signals.
14. The system of claim 13 wherein the reference signal is a pilot and a preamble signal.
15. A method of locating one or more radio frequency identification (RFID) tags comprising:
illuminating at least one RFID tag by a plurality of transmit antennas using interrogation signals at a plurality of frequencies;
receiving a plurality of information signals from the illuminated at least one RFID tag by a receive antenna, where the plurality of information signals include information signals generated in response to interrogation signals sent at different frequencies from each transmit antenna;
determining a group delay for each group of received information signals from the at least one illuminated RFID tag received by the receive antenna that were sent in response to interrogation signals from each transmit antenna;
determining the path length between the receive antenna, the at least one illuminated RFID tag, and each of the plurality of transmit antennas using the determined group delays of the received information signals;
determining a plurality of ellipses based on the locations of each of the plurality of transmit antennas, the location of the receive antenna, and the determined path lengths; and
identifying a location of the at least one RFID tag based on the determined ellipses.
16. The method of claim 15 further comprising transmitting an activation signal from a reader to an exciter, the reader and exciter sharing a common geometric characteristic relative to each other, the reader comprising the receive antenna, and the exciter comprising at least one of the plurality of transmit antennas.
17. The method of claim 16 wherein the shared common geometric characteristic is an ellipsoid wherein the reader and the exciter are foci of the ellipsoid.
18. The method of claim 15 wherein identifying the location of the at least one RFID tag is based on a frequency derivate of the received information signals.
19. The method of claim 15 wherein identifying the location of the at least one RFID tag is based on a ratio of the phase derivate versus the frequency derivate.
20. The method of claim 15 wherein identifying the location of the at least one RFID tag is based on a read rate derivate of the received information signals.